This spell is getting put in a wand in my Wit's End adventure for the Five Shires. Its name, of course, comes from the old Scott Adams adventure games ("the opposite of Light is Unlight") and will be used by a crazed shipwrecked halfling pirate on the PCs' light source(s) as they enter a dark cave that will be occupied by a shadow grue once the room goes dark.
(The pirate will shut a light-tight hatch when he flees from the ledge above cave floor.)
But I figured that this spell might show up later on IMC, so I might as well make this as workable as I can. I envision this being a rare spell only because it's of limited use, but is otherwise commonly available at the GSoM and at other magical schools, as well as being available through divine magic.
Unlight
by Beau YarbroughUnlight
Transmutation
Level: Assassin 1, Blackguard 1, Clr 1, Wiz 1 Components: V, S, F
Casting Time: 1 action
Range: Close (25 ft. + 5 ft./2 levels)
Target: All light sources within a 20 ft. radius Duration: Instantaneous
Saving Throw: None
Spell Resistance: No
This spell causes light sources to be suddenly extinguished in a 20-foot radius.
Light sources automatically affected include (but are not limited to) candles, torches, lanterns, tindertwigs, dancing lights, light spells, and faerie fire.
Larger light sources -- such as bonfires, sunrods, continual flame and daylight spells -- require a dispel check. The dispel check is 1d20 + 1 per caster level (maximum +5) against a DC of 11 + spell level + the spell's caster level for spells. For other light sources, use the following DCs:
Light source DC
Bonfire 15
Sunrod 20
Nothing prevents a light source that can be relit being relit after being affected by this spell, and light sources beyond the area of effect are unaffected -- thus, sunlight, moonlight and starlight are never affected by this spell.
Focus: An extinguished black or grey candle.